Don't put '+' button in front of basic type fields in Add Fields By Origin

Description of problem:
This is not a bug, but request for echancement. When you add Basic type (Bool, Integer, Date etc.) as Field Data origin, and then you go to Add fields by Origin, there is a '+' button rendered in front of each data origin, even though there is nothing to expand with this plus button.
This can be confusing to the users, because when they click the plus, the list moves a bit, but nothing else happens. It looks, that there is something broken, even though everything is ok.

Observe the problem in the video attached.

Version-Release number of selected component (if applicable):
BPMS 6.0.1 CR2

How reproducible:
Always

Steps to Reproduce:
1. In Form Data Origin add some origins 'From Basic Type'
2. Go to Add fields by origin

Actual results:
The + button rendered in front of each data origin does nothing, because there is nothing to expand (Basic types represent primitive values)

Expected results:
There should be no + button, just blank red branching, as is the case for fields of complex type (from Data model, from java class). See screenshot of how it should look in ideal case.